The present invention relates to packages for protecting comestibles and to the polyesters from which such packages are made. More specifically, it relates to films and molded containers which are formed from such polyesters.
Presently there is a strong interest in the packaging industry for protecting comestibles, such as foodstuffs, medicines, and especially carbonated beverages, by enveloping the substances in packages which are formed from various polymers. One polymer in which there is an especially strong interest is polyethylene terephthalate. Containers formed from this material, which may be biaxially oriented, possess many desirable characteristics. Molded biaxially oriented containers which are formed from polyethylene terephthalate and certain copolyesters are disclosed in U.S. Pat. No. 3,733,309. While molded containers formed from polyethylene terephthalate have, as indicated, many desirable characteristics, there is a need in the art to provide improved polyester containers which will have gas permeabilities which are lower than those of containers formed from polyethylene terephthalate. Such improved containers would be much more versatile in their utilization and allow the containers to be used to package substances for which the polyethylene terephthalate containers may not be suitable.
The present invention provides a novel polyester which is suitable for use in forming packages for protecting comestibles. The present invention also provides improved containers made of the polyester which exhibit improved resistance to gas permeability. The polyester of the present invention comprises a diacid component comprising 1,4-phenylenedioxy diacetic acid, 1,3-phenylenedioxy diacetic acid, 1,2-phenylenedioxy diacetic acid and mixtures thereof. Containers formed from the novel polyester exhibit a desirable balance of physical properties, including improved gas barrier properties, which render them advantageous for use in the packaging of comestibles.
U.S. Pat. No. 3,522,328 discloses copoly(ester-amides) wherein the amide moieties may comprise p-phenylenedioxydiacetic acid. The patent neither discloses nor suggests the use of p-phenylenedioxy diacetic acid in the preparation of polyesters nor the use of such polyesters as containers having improved gas barrier properties.